Five projects were identified in the grant application. The first project was concerned with the generation of active oxygen by liver microsomes during microsomal electron transfer. The second project was concerned with the stoichiometry of the reactions in which active oxygen was generated. The third project was concerned with the use of inhibitors of various microsomal enzymes to trace the routes of microsomal reactions. The fourth project was concerned with the mechanism and route of epinephrine oxidation. The fifth project was concerned with attempts to learn the nature of enzyme bound active oxygen, using quenchers, such as singlet oxygen or hydroxy radical quenchers.